Melaena refers to a black tarry stool, which usually occurs as a result of upper gastrointestinal bleeding.
They have a characteristic colour and offensive smell, which is due to the alteration and degradation of blood by intestinal enzymes and bacteria.
In this article, we shall look at the differential diagnosis, clinical features and investigations for malaena.
Melaena usually occurs as a result of an upper gastrointestinal bleed (rarely it can be due to bleeding in the small intestine or right colon). Upper GI haemorrhage has a number of causes – the most common of which are peptic ulcer disease, liver disease, and malignancy:
Peptic Ulcer Disease
Peptic ulcer disease is the most common cause of melaena, and should be suspected in those with:
- Known active peptic ulcer disease.
- H. Pylori positive.
- History of NSAID or steroid use.
- Previous epigastric symptoms suggesting peptic ulceration.
Classically, the most significant bleeding will occur if an ulcer erodes through the posterior gastric wall and into the gastroduodenal artery. However, in reality, extensive bleeding can occur with the erosion of any blood vessel.
Oesophageal varices refer to dilations of the porto-systemic anastomoses in the oesophagus. They most commonly occur due to portal hypertension, secondary to liver cirrhosis – and are very prone to rupture.
Thus, the most common underlying cause for oesophageal varices is alcoholic liver disease. Any significant melaena in a patient with a known history of alcohol abuse should be investigated as urgently as possible.
Upper GI Malignancy
Ulcerating oesophageal or gastric malignancies can first present with melaena, causing a gradual flow of blood that may present prior to any other cancer-associated symptoms.
In the assessment of any patient with melaena, it is important to inquire about other upper GI symptoms, weight loss, or relevant family history – which may point towards a diagnosis of malignancy.
Other less common causes of melena include gastritis or oesophagitis, Mallory–Weiss tear, Meckel’s diverticulum, or vascular malformations (e.g. Dieulafoy lesion).
The key facts to ascertain from a history of melaena are:
- Colour and texture of the stool – jet black, tar-like, and sticky.
- Associated symptoms – including haematemesis, abdominal pain, or a history of dyspepsia, dysphasia or odynophagia.
- Past medical history – including smoking and alcohol status, and inflammatory bowel disease.
- Drug history – use of steroids, NSAIDs, anticoagulants, or iron tablets.
A PR exam is essential to confirm the melaena, as well as a full abdominal exam assessing for epigastric tenderness or peritonism, hepatomegaly, and evidence of stigmata of liver disease.
Investigations should be tailored to the specific presentation, but a generic outline would involve a structured approach as discussed below:
- Routine bloods (FBC, U&Es, LFTs, and clotting):
- Any acute bleed may not initially show an anaemia in the full blood count.
- Liver function tests may reveal underlying liver damage as a potential cause.
- Any drop in haemoglobin and rise in the urea:creatinine ratio* is very indicative of an upper GI bleed.
- All patients with melaena should have a Group and Save requested; those with significant melaena (especially suspected variceal bleed) should have at least 4 units of blood cross-matched.
- Arterial blood gas:
- Useful in bleeding or septic patients, especially for the pH, pO2, pCO2, and lactate, for signs of tissue hypoperfusion.
- Oesophagogastroduodenoscopy (OGD):
- The definitive investigation in most cases of melaena. It also forms part of the management in cases of ongoing unstable bleeding.
- Occasionally colonoscopy or capsular endoscopy may be required to determine the site of bleeding.
*Digested haemoglobin produces urea as a by-product; this is readily absorbed by the intestine and consequently upper GI bleeds can show as a rise in urea levels
Glasgow-Blatchford Bleeding Score
The Glasgow-Blatchford Bleeding Score can be used to determine the risk and severity of the current episode of upper GI bleeding and the urgency required for endoscopy.
It is a score that is based on clinical and biochemical parameters. Importantly, it can identify patients of low risk who may be suitable for discharge and outpatient investigation.
Interpretation will vary across endoscopy departments, but scores ≥6 have been associated with a >50% risk of needing an intervention.
Once endoscopy has been performed, this score is typically replaced with the Rockall risk score.
|Known Hepatic Failure||Present|
In any critically unwell patient, an A-E approach should be used to stablise the patient before considering definitive management steps.
Once the patient is stable (or initial resuscitation attempts have proved ineffective and more invasive management for resuscitation is required), an endoscopy should be arranged.
During the OGD, a range of therapeutic options are available, depending on the underlying cause:
- Peptic ulcer disease – requires injections of adrenaline and cauterisation of the bleeding. High dose intravenous PPI therapy should be administered (e.g. IV 40mg omeprazole) to control the acidic environment.
- Oesophageal varices – management should be swift and performed at the same time as active resuscitation, including the use of blood products.
- Endoscopic banding is the most definitive method of management but can be technically difficult.
- Prophylactic antibiotic therapy should be initiated, alongside somatostatin analogues (e.g. terlipressin or octreotide), acting to reduce splanchnic blood flow and hence reduce bleeding.
- A Sengstaken-Blakemore tube can be used in severe or uncontrollable cases, inserted to the level of the varices and inflated to compress the bleeding to act as a temporary control.
- Upper GI malignancies – will require biopsies to be taken and a definitive long-term surgical and oncological management to be put in place
Blood transfusions should be given to those with low Hb or ongoing significant blood loss. Correct any deranged coagulation as appropriate, such as use of appropriate reversal agents if the patient is on any anti-coagulants or use of FFP for impaired liver function.